Alloy



.l Altman l .1

Patented Feb. 3, 1942 Cross llefernE NoDr'awing Application October 21,1939; seriamcsooss 1 Clain'n' 01. 75-160) This invention. relates to alloys. and has for. its. principal object the. provision. of animproved copper-base alloy of the copper-aluminumesilicon type. l I

Copper-aluminum -silicon; alloys. have. been known. for many. years. These all'oyslarehard;

and strong, they are. resistant to corrosion. under a widevari'ety of conditionsand they are lighter in weight than alloys of copper and silicon containing noaluminum. They are, however, somewhat difficult to machine, and for this reason are not wholly satisfactory for use in the manufacture of machined parts on automatic screw machines. I

We have found that the machinabili-ty of alloys comprising chiefly copper with'relatively small amounts of silicon and aluminum is materially improved by the addition of a small amount of lead. The presence of lead in the alloy does not appreciablyimpair its hot and cold working prop.- ertie sp'and the improved machinabil'i'ty imparted by the-lead greatly increases usefulness of the alloy.

Copper-base alloys .of aluminum and silicon. usually contain from 0.25% to 11% aluminum,v from 0.1% to 3.5% silicon, and the balance chiefly copper. These percentages and others throughout this specification and the appended claims are by'weightiof' the alloys. An alloy of this general type embodying our invention may comprise from 0.25% to 11% aluminum, from 0l1'%1t'o' and the hole formed was smooth and .free. of

burrs.

The four alloys listed in the above-tabulation were tested for forgeability. AlloysA andB, containing a relatively high proportion of aluminum, both displayed excellent forging properties, but alloys 0 and D, containing a lower percentage of alurninum,vwere less satisfactory in this respect. Alloy B', therefore, was the most satisfactory'of these rear alloys for general use.

" Other metals maybe incorporated in the alloy for the purpose'of imparting special properties,-

suchas' improved casting, forging and working properties. Manganese is 'aparticularly desir able addition', for it improves the casting qualities of these alloys, apparently, by increasingfluidity of the melt and-bringing about suitable shrinkage during solidification Manganese "also increases the strength and toughness of the alloy; and improves its- 'hot working (forging, rolling, extrudingetc properties by preventing the appearance of minute edge cracks inth'e hot-- wrought article. From 0.1% to 3% manganese maybe added tothe lead-bearing alloys described' above to secure these benefits.

Iron-'may'be incorporated in the" alloy 'toin-' crease its hardnessfand tensile strength and alsoto-ma-ke the alloy easierto} hot" Work by increas ing the me working temperature" range. Iron refines the gra instructure of the new alloy, keeping it uniform and fine 'Il'iese benefitsmay be L jNi'ckel-maybe'present in the alloy in amounts pftFs-ci. but it does not particularly improve:

sov is much moresu-itablegstock for use; in, autoy matic screw machines. 1

The following tabulation indicates: the im-" proved machinability of the new lead-bearing a1- loy: 1

Alloy A B C- D 1 1 Balance Balance Balance Balance Excellent Fair Excellent Fair chips and of the hole formed. The bars containa ing no lead could not be drilled as rapidly as the lead-bearing bars, and were discolored near the point of drilling when the drill was forced. The chips from the lead-bearing bars came away more cleanly than from the bars containing no lead,

achieved by incorporati-ng' from 0.25 to-4 iron in the lead-bearing alloys described above. Such amount of iron does 'not" appreciably impair the machinability of the alloy;

the alloy. The" presence of a -smal-lamount of zinc in'thea-l-loy'isnot objectionable; 'I-ir-r also ,may be present -i-n-the-alloy in small-amounts ofthe-order or-0.25%, but experience indicates that larger amounts of tinare likely to makethealloy subject to cracking. The alloy may in addition contain small amounts of impurities, such as elements commonly present in commercial copper and other components of the alloy, without detrimental efiect.

Particularly satisfactory free-machining alloys for general use as screw machine stock cornprise from 5% to 9% aluminum, from 0.5% to 2.5% silicon, from 0.75% to 1.75% lead, and thebalance chiefly copper. If manganese is employed, it is generally preferred to use it in amount from 0.5% to 1.5%, and iron, if employed, preferably is added in amount from 0.5% to 4%. Alloys prepared within these preferred percentage limits possess the best balance of' properties for general use where a strong, corrosion-resistant relatively light, free-machining metal is desired.

The maximum amount of silicon it is desirable seaita W to employ in order to obtain alloys having optimum hot and cold working properties varies inversely with the amount of aluminum present. For example, an alloy containing as little as 0.25% aluminum may contain as much as 3.5% silicon, whereas an alloy containing as much as- 10% aluminum preferably contains only about 0.5% silicon. Manganese and iron, if present in the alloy, are additive to the aluminum in so far as determining the optimum maximum silicon content is concerned. In the following tabulation preferred maximum ratios of silicon to aluminum (plus manganese and iron, if present) are set forth by way of example:

Percent Al Preferred Percent (+Mn+Fe, max. percent if present) Si 5 3. 5 Balance. 6 3.0 Do. 7 2. 5 Do. 8 2. Do. 9 1. Do. 10 0.5 Do.

Alloys according to the invention may be worked at a red heat by rolling, forging, extruding, pressing and stamping operations and therefore may be fabricated into various articles at moderate expense. The new alloys may be coldrolled or cold-drawn to a limited extent by the usualprocedures for cold working the more refractory copper-base alloys.

creased if the alloy is hot worked and then allowed to cool slowly in air before subjecting it to the cold working operation. The alloys are hardened by cold working, but may be annealed Per cent Copper 88.75 Aluminum 8.50 Silicon 0.75 Lead- 1.00 Manganese 1.00

This alloy was prepared by melting together The amount of reduction attainable by cold working may be in-v weighed quantities of the several components. The molten alloy was cast into a suitable shape which was extruded hot and then drawn cold into a round rod of 1% inches in diameter. In this form it possessed the following properties:

Tensile strength 84,000to98,000lb./sq.in. Yield strength in 0.5% I

extension 60,000 lb./sq. in. Elongation in 2" 12%. Rockwell hardness (B scale) 100. Brinell hardness 210. Density 7.43 gm./cc.

This alloy was found to machine easily atcommercial speeds without overheating and without burring or tearing. It possessed good hot-forging properties.

The beneficial effect of iron on the forgeability of the new alloy is indicated by the following ex- Discs one inch long were cut from one inch diameter bars formed from each of these alloys and were hot-forged at 750 C. and at 850 G. into lozenges approximately one-quarter inch thick. The hot-forgeability of these alloys, and their machinability, is indicated in the following tabu- We'claim':

A copper-base alloy comprising about 8.5% aluminum, about 0.75% silicon, about 1% lead, about 1% manganese, and the balance substantially all copper.

I CHARLES H. DAVIS.

ELIWER L. MUNSON; 

